THE MAJORITY OF ICE LOSS FROM ANTARCTICA EMANATES FROM THE WEST ANTARCTIC ICE SHEET WHICH MODEL SIMULATIONS SUGGEST IS IN THE EARLY STAGES OF COLLAPSE. THE ICESAT-2 MISSION WILL MEASURE THE CHANGE IN ELEVATION ASSOCIATED WITH THESE LOSSES WITH UNPRECEDENTED DETAIL. WEST ANTARCTIC ICE LOSS HOWEVER HAS BEEN OCCURRING FOR MULTIPLE DECADES WITH PATTERNS OF THINNING THAT CAN EVOLVE RAPIDLY.THIS MEANS THAT THE NOMINAL 5-YEAR DURATION OF THE MISSION PROVIDES A RELATIVELY NARROW TEMPORAL WINDOW WITH WHICH TO UNDERSTAND LONGER-TERM EVOLUTION. THIS LIMITED INTERVAL MEANS THAT EXTENDING THE OBSERVATIONAL RECORD OVER A LONG A PERIOD AS POSSIBLE IS OF PARAMOUNT IMPORTANCE FOR UNDERSTANDING CURRENT AND FUTURE ICE LOSS FROM WEST ANTARCTICA. TOWARD THIS GOAL WE WILL COMBINE DATA FROM NUMEROUS MISSIONS (ICESAT CRYOSAT-2 ICEBRIDGE AND WORLDVIEW) TO PRODUCE AN ~15-YEAR BASELINE DATA SET FOR WEST ANTARCTICA THAT CAPTURES THE SPATIO-TEMPORAL PATTERNS OF ELEVATION CHANGE FROM 2003 THROUGH THE LAUNCH OF ICESAT-2. WE WILL MAKE THESE ~ANNUALLY RESOLVED MAPS OF THINNING AVAILABLE TO THE SCIENTIFIC COMMUNITY FOR STUDYING NUMEROUS ASPECTS OF ICE-SHEET ELEVATION CHANGE.FOR THIS STUDY WE WILL USE THE PRODUCTS THAT WE PRODUCE TO STUDY HOW PATTERNS OF DYNAMIC THINNING EVOLVE THROUGH TIME AND WHAT PROCESSES GOVERN THIS EVOLUTION. SUCH UNDERSTANDING IS IMPORTANT TO PROVIDE A CONTEXT IN WHICH TO INTERPRET THE OBSERVATIONS THAT ICESAT-2 WILL PROVIDE. AS A FIRST STEP WE WILL ANALYZE THE ELEVATION-CHANGE HISTORY TO CHARACTERIZE HOW THE SPATIAL PATTERNS OF THINNING EVOLVE THROUGH TIME FOLLOWING EVENTS SUCH GLACIER SPEEDUP IN RESPONSE TO GROUNDING-LINE RETREAT. ALREADY OUR PAST WORK HAS SHOWN THAT THESE PATTERNS CAN EVOLVE RAPIDLY (RELATIVE TO THE SCALE OF A 5-YEAR MISSION) AND THAT THE PATTERNS OF MODELED CHANGE ARE SENSITIVE TO THE FORM OF THE ASSUMED MODEL. FOR EXAMPLE THE EXPONENT OF THE SLIDING LAW CAN LEAD TO SIGNIFICANTLY DIFFERENT PATTERNS OF THINNING.THUS ONCE WE HAVE A GOOD CHARACTERIZATION OF THE PATTERNS OF CHANGE WE WILL USE OUR NEW TIME SERIES TO CONSTRAIN ICE-FLOW MODELS TO UNDERSTAND WHAT THE DOMINANT PROCESSES ARE THAT CONTROL THE OBSERVED PATTERNS OF THINNING (IN SOME CASES THICKENING). THIS WORK WILL INVOLVE SEVERAL CASE STUDIES OF GLACIERS IN THE MOST RAPIDLY THINNING AREAS. IN PARTICULAR WE WILL FOCUS ON HOW RAPIDLY CHANGES NEAR THE GROUNDING LINE OF PINE ISLAND AND THWAITES DIFFUSE INLAND. ALTHOUGH THINNING PREDOMINATES IN WEST ANTARCTICA WE ALSO WILL EXAMINE KAMB AND WHILLANS ICE STREAMS WHERE THICKENING DUE TO SLOWDOWN OR FULL STAGNATION HAS MITIGATED SOME OF LOSSES ALONG THE AMUNDSEN COAST. IN ADDITION WE WILL USE THE OBSERVATIONS AND MODELS TO BETTER UNDERSTAND THE RELATIVE ROLES OF DYNAMIC THINNING AND SURFACE MASS BALANCE IN PRODUCING THE RECENT OBSERVATIONS OF INCREASED THINNING ALONG THE BELLINGSHAUSEN COAST. THROUGH THESE CASE STUDIES WE WILL GAIN A MUCH A BETTER UNDERSTANDING OF WHAT COLLECTION OF PROCESSES IS DRIVING ICE LOSS IN WEST ANTARCTICA. MOREOVER BY RIGOROUSLY CONSTRAINING THE MODELS TO REPRODUCES CHANGE OVER A DECADE IN HALF WE WILL IMPROVE OUR ABILITY TO PROJECT ICE SHEET LOSS IN THE COMING DECADES AND CENTURIES.